1. Field of the Invention
This invention relates to connecting rods, for example of the type used in reciprocating piston engines, and in particular to cast connecting rods.
2. Discussion of the Related Art
Connecting rods used in reciprocating piston and internal combustion engines have great stresses imposed upon them in operation of the engine and therefore must be very strong, and preferably of light weight. In the case of connecting rods, the ends of the connecting rod must be machined for the bearing bores, one for the crank pin and the other for the wrist pin, and also typically the crank end of the connecting rod also must be drilled and tapped so as to secure the crankshaft bearing cap of the connecting rod to the remainder of the connecting rod.
Forming the connecting rod with traditional materials that possess the required combination of strength and weight can result in difficult machining of the connecting rod, and in particular in increased wear and tear on the tools and tooling used in the machining operations. Hence, the typical solution in prior art connecting rods was to compromise strength and weight for machinability.
For smaller engines, the material of the connecting rod may be a cast aluminum alloy. Such material is machinable, but can be marginal for strength, and also may have a significantly different coefficient of thermal expansion than the crankshaft or the wrist pin.
Thus, a need exists for a connecting rod construction that is machinable, strong, lightweight and thermally compatible with the crankshaft and wrist pin materials, and economical to manufacture.